“The combined air forces will strengthen their battle readiness under the current situation when tension rises over the Korean peninsula.”

South Korean Air Force

It comes as the allies are winding up separate annual military drills which began in late February, and have been denounced by North Korean authorities as rehearsals for invasion.

In a pointed protest at the exercises, Pyongyang carried out a series of rocket and missile launches, capped by its first mid-range missile test since 2009 on March 26.

The two Koreas also traded artillery fire across the tense Yellow Sea border on March 31, after the North dropped around 100 shells across the maritime boundary during a live-fire drill.

The exchange followed a North Korean warning that it might carry out a “new” form of nuclear test – a possible reference to a uranium-based device or a miniaturised warhead small enough to fit on a ballistic missile.

The United States, South Korea and Japan, meeting in Washington on Monday, condemned the ballistic missile tests and urged the North “to refrain from further threatening actions”.